As a semiconductor laser element, a spatial horizontal single mode type one and a multi-mode type one are always known. In a single mode type semiconductor laser element, a waveguide with a narrow width is formed to limit the oscillation mode in the waveguide to only a single mode. However, when the width of the waveguide is narrow, the area of the emitting end also becomes small. When the laser beam density becomes excessively high at the emitting end, reliability of the semiconductor laser element is influenced. Therefore, the single mode type semiconductor laser element is suitable for applications where relatively low output laser beams are used. An example of the single mode type semiconductor laser element is the semiconductor laser device disclosed in Patent Document 1. This semiconductor laser device is a single mode type semiconductor laser, of which object is increasing the laser beam intensity by expanding the width of the waveguide.
In the multi-mode type semiconductor laser element, on the other hand, a plurality of modes may coexist in the waveguide, so a wide waveguide can be formed. Therefore, the area of the emitting end can be large, and relatively high intensity laser beams can be emitted. This multi-mode type semiconductor laser element is suitable for applications where relatively high output laser beams are required.
The multi-mode type semiconductor laser element, however, has the following problem. A plurality of modes coexist in the waveguide, so the emission pattern of the laser beams to be emitted from the emitting end is disturbed, and the emission angle becomes relatively large. So the shape of the lens to condense or collimate the laser beams becomes complicated, and desired laser beams may not be acquired or the manufacturing cost may become high (lens becomes expensive).
An example of a technology to solve this problem of a multi-mode type semiconductor laser element is the resonator disclosed in the Patent Document 2. FIG. 1 shows the structure of a conventional resonator, and the area (a) is a plan view showing the configuration of this resonator. The resonator 100 has two regions 102a and 102b in the active layer 101. In the area (b) of FIG. 1, the refractive index distribution in the VII-VII cross section in the area (a) and the VIII-VIII cross section in the area (a) are shown. As shown in the area (b), the refractive index n2 in the regions 102 a and 102 b is lower than refractive index nil in the other area of the active layer 101. The regions 102a and 102 b are formed in the active layer 101 at an angle at which the lights L, vertically reflected at the emitting end 100 a and the reflecting end 100 b, are totally reflected on the side faces of these regions 102 a and 102 b. In Patent Document 2, a single mode oscillation is attempted to be implemented without limiting the waveguide width by limiting the optical paths of the lights L resonating in the active layer 101 using this configuration. Patent Document 1: Japanese Patent Application Laid-Open No. Hei10-41582Patent Document 2: International Publication No. 00/48277 Pamphlet